1. Field of the Invention
This invention relates generally to one-way pressure relief valves that are applied to packaging for products, such as coffee, and more particularly to improved pressure relief valves that do not require a lubricant such as oil.
2. Background Art
Engel et al. U.S. Pat. No. 7,178,555 issued Feb. 20, 2007 discloses a one-way pressure relief valve attachable to product packaging to vent pressurized gases from the packaging. One-way pressure relief valves, such as the PLITEK PLI-VALV PV-28 pressure relief valves, are applied to packaging for products, such as coffee, to allow unwanted gases to vent from the packaging while sealing out atmospheric gases. Such valves may vary in material and construction depending on the packaging application. They may be plastic or foil, and are generally self-adhering, thin, low profile designs supplied on a non-tearing polyester or paper liner. The valves are generally attached to the customer packaging with a heat sealed or pressure sensitive adhesive. An adhesive on the back side of the valves may initially mount them on the liner, until the valves are removed immediately prior to the application to the packaging, and then provides for attaching the valves to the packaging. In operation on the packaging, the valves open at a target pressure and then close at a lower target pressure, the values of which are dependent on the packaging application, after pressure inside the packaging drops. The valves vent unwanted gases and seal out atmospheric gases from rigid or flexible packaging or other enclosures. One advantage of such valves is that they allow a product such as coffee to be packed immediately after roasting and grinding to preserve freshness. Such one-way pressure relief valves allow a product such as coffee to degas during packaging and shipping, while reducing oxidation of the product. Use of such valves permits elimination of a bulk degassing process of the product prior to packaging. This not only speeds the overall process, saving time and money, and space, but also reduces exposure of the product to oxidation. Thus the product, such as coffee, is provided to consumers at a greater level of freshness and quality.
While not expressly disclosed in prior art such as Engel et al. U.S. Pat. No. 7,178,555 a sealing lubricant such as a silicone or graphite impregnated oil has to be injected between the membrane layers of the valve structure to ensure true one way functionality. Such required injection of a sealing lubricant is normally done just prior to applying the valve to the packaging. The dry strap membrane of such prior art valves is permitted to flex away from an opening to vent unwanted gases upon the inside of the packaging reaching the application determined opening pressure, and then when the pressure drops to the application determined closing pressure, the dry strap in cooperation with the sealing lubricant applied during the process of affixing the valve to the packaging, flexes back toward the opening to provide the one way valve function to prevent atmospheric gases from entering the packaging.
An example of such an application of lubricant is disclosed in Hoffman et al. U.S. Pat. No. 7,472,524 issued Jan. 6, 2009. Without such a sealing lubricant such prior art valves, while permitting gases to vent, would not properly close and would allow undesired atmospheric gases, including oxygen, into the packaging. The step of lubricating the valves adds time, cost and another factor to control in the process of applying the valves. After the injection of silicone, graphite impregnated oil, or some other sealing lubricant, the pressure relief valve is then attached to the packaging. While the oiled valve is often attached to the outside of the packaging, there may be instances in which it is desirable to put the valve inside with the product. Accordingly, there is a need for a one-way pressure relief valve that does not require the addition of a lubricant.
There also remains a need for a pressure relief valve that is protected from becoming fouled by fine particulate, including the product it is intended to keep at its highest quality.
It would also be desirable for certain products, and/or for packaging intended to be used in certain environments, to have a pressure relief valve in which liquid is prevented from penetrating the valve seal layer.